The present invention generally relates to moldable materials and, more particularly, relates to a method for making a moldable material. Most particularly, the invention relates to a method for efficiently making a cost-effective pliable moldable material having a high tensile strength and high modulus.
It is well known to form a strand from a collection of fibers. This can be achieved, for example, by passing molten material (e.g., molten glass) through a plurality of orifices in a tip plate of a fiber forming bushing. Fibers formed by the fiber forming bushing are linearly pulled and gathered together to form one or more strands. The strands are typically wound on a collet to form packages, which subsequently can be used to produce various products. For example, a roving can be formed from a single strand (i.e., a single end roving) or a plurality of strands that are linearly pulled and gathered together (i.e., a multi-end roving). A plurality of rovings can be wound on a wrap wheel and then cut to form a hank, which can be used as a charge of material for making or molding a laminate or final composite part. A composite part formed from fibrous materials are preferred in applications where it is desirable to minimize the weight of the composite part.
A broad range of composite parts is produced from fibrous materials. Such composite parts differ in their requirement for tensile strength (i.e., how strong a material is when pulled upon) and modulus (i.e., how well a material resists deformation). Some composite parts require a high tensile strength and a high modulus. For example, lightweight composite leaf springs having a high tensile strength and a high modulus are preferred in high-performance motor vehicles. Conventionally, such leaf springs are molded from a charge of material formed from glass fiber strands impregnated with an epoxy resin. The glass fiber strands are impregnated by passing the glass fiber strands through a bath of epoxy resin. As a result of the impregnation, the charge of material has good wet out, (i.e., the glass fibers and epoxy resin are in close contact and the resin to glass ratio is appropriate, about 70% glass by weight and about 30% resin by weight). In a subsequent filament winding process, heat and pressure are used to cure and form the charge into a leaf spring. The filament winding process is well known in the art and works quite well but it does have its limitations. Often, the impregnated glass fiber strand is quite sticky and excess resin usually comes off the glass fiber strand and thus is wasted. In addition, the incorporation of other fibers with glass epoxy is very difficult because every type of fiber has its own unique set of processing characteristics.
What is needed is a lightweight, cost-effective charge of moldable material that is dry and easily processable and can very easily accept other fibers into the composite to modify and improve the composite part.
The present invention is directed toward a method for making moldable material comprising the initial step of providing a composite material comprised in part of an epoxy. A high performance strand is then distributed in the composite material to form a moldable material. Lastly, the moldable material is heated sufficiently to cause the composite material and the high performance strand to stick at least slightly together without melting the epoxy.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.